Directional wave energy receiving system



3 Sheets-Sheet 1 G. F. ASBURY, SR

DIRECTIONAI.. WAVE ENERGY RECEIVING SYSTEM Filed Dec. 8, 1952 June 28,1960 IIIZP l l l l llllv INVENTOR G EORGE F. AS BURY,.SR

(bg J- ATTORNEY5 June 28, 1960 G. F. AsBURY, SR 2,943,322

DIRECTIONAL WAVE ENERGY RECEIVING SYSTEM Filed Dec. 8, 1952A 3Sheets-Sheet 2 |NPuT i 'ioUTPlT l 42 I l K i I 43 V55 Elil L HP? l l i|31 l L VARIABLE 5h 6M PHASE SHIFTER I swEEP F'XED oscILLAToR i vAR|ABLEI I DELAY l DQ/ I I OUTPUT FRo v| al FROM e2 INVENTOR BY i l ATToRNEYJune 28,A 1960 G. AsBuRY, sR

DIRECTIONAL WAVE ENERGY RECEIVING SYSTEM Filed Deo. s, 1952 3Sheets-Sheet 5 3o 9o |50 21o 27o 33o VARIABLE v ZOSN DELAY VARIABLEINVENTOR GEORGE F. ASBURYSR.

@{vll I ATToRNEYs This `invention-relaties-'to -wavefenerg-vreceiving'xsystems'.

nitedStat-es Patent] More particularly it relates-toa directional waveenergy receiving system wherein vthe `direction'of optimum reeeption ofthe :receiving-.system-can be scannedthrough 3 6G- or' azimuth withoutmechanical movement of the wavesignal receiving array.

ilt is an.-objectl .of this invention to provide a signalfreceivingsystem which -is exclusively vresponsive .tozsignals received from-aselected directional zone.

It is another object .to provide a directional .receiving system in`which the direction from which .signals-are selectively -receivedcan `be-varied through 360 -of azimuth without physical movement-.of -thesignal receivin'gmeans.

fit is another object` to 'provide-,a .receiving system in which thedirectiontrom` whichsignals are selectively received `can be varied at astation :remote from the signal receiving means. v -H It is anothervobject -to--providea receiving vsystem-rin which the direction .fromwhich signals `are selectively received can be varied by selectivelyadjustingethe time relationship of received signals in a:predetermined-,man- 11er.

It is another object to provide a receiving .system in which the widthof the selected directional zone of reception can be variedindependently of the .frequency of rei ceived signals, ata station.remote from the signal receiving means.

These and other objects and features ofthe-present invention will appearmore fully .hereinafter from the following detailed descriptionconsidered in connection-withy the accompanying drawings, which discloseone-embodiment of the-invention. It is expressly understood, how` ever,that: the drawings are designed for purposes of illustration only andnot asadeinition ofthe limits' of the invention, for whichreferenceshould'be hadto thevappended claims.

In the drawings:

Figure 1 is a schematic blockdiagram of a receiving-` system constructedin-accordancewith the present-inven tion.

Figures 2, 3' and 5 are schematic. diagrams ofportionsoi the systemshown in- Figuregl. v

Figure 4 is a graph useful inl explaining the operation of thisinvention.

Brieily, theV presentinvention provides 'means for-.receivingselectively only signals whose arrival-times-at threetriangularlydisposed `receiving elementsbear a particularselected relationship.Specilically the signals arriving. at the three elements are-delayed-byvarying-amounts `of time as necessary to bring-them-.into coincidence,-the varying amounts of delay required providing, a measureof thereceived signal direction ofarrival. Moreover,.

time delays imparted lto-signals-received4 by each-ofthethree receivingelements` can be varied relative 'to-one:`

another` in an orderly mannerto vary smoothly the'idirecf tion f fromwhich .signals-k are selectively received,. s"o thateifectively 360"of."` azimuth can bef scanned withoutf any.`

physical rotation of the receiving element array, by

2,943,322 Patented "June 28, i960 a ce A"riierly varying 'thetime 'delayVa"ss-ocia'ted 'with each re- 'angle ABC' should not be longer 4than onewavelength ofV vthehighest frequericyl4 signal to he received,lirl-order to avoid'a'rribiguitiesin processingthe received signals, as'will be apparent hereinafter. With the, three receiving elements ,'sooriented itlv'vill be-*ap'parent that it is possible to ascertain theorientation'of the wavefront of anyV sig'- nal intercepted by uthe'receiving "array by measuring the relative times of 'anivalfofthereceivedsignal at the three dil'erent elements.YConversely:byrecovering from all the signals intercepted by thethree-element array 1,` only those sign-als which arrive at thediieren't elements: A, BY and C 'in-a preselected time relationship,itis possible to recover selectively 'only signals Ywhose wavefronts'have aparticular selected orientation, ie., Vvv'ljiich "arrive froma'particular selected tii'rectionfor bearing; For example, it-'vw'ill"be apparent that a signal which arrives first at element A, Vand I aterarivessimultaneously at elements B'v 'and C, 'comes froma directiondened by 'a line 'be tween'the'cen'ter Oofthe't'riahgle and element A,and fit isl possible to recover selectively onlys`i`g`n`alsjfromthisdirection by Y'recovering only 'signals` whose l"arrival `times atthe"three-receiving-elements are sorelated. Y n u Signals interceptedthe receiving array 1 are corrveyedihrough v`av common communicationlink 4, such as a radio link or r'e transmissionilin, 'tothe remainderof the 'gtial receiving 'system which may be located;at v'a statio emoteffroin thereceivingl array. Fromthe output of theA E:om'muiii'c'atic'mlliirk 44, Ithe' signal from receiving element is fed through` amplifier5 to a-pulse generator 6; In pulse generator 6 the received signal'isconverted to' the form of a train of pulses, 4one for eachfcycle of thereceiver signal. Purse gent-rami; `s may be or any conventional form,capable of generating a pulse at the saine point'in each cycle of `aVwavetrain signal, for 'example, a s'at'rable reactor.V 'Ihe'outputpulsesy fromY pulse generator 76' are-fed to a pulsewiden'er 7, whichfor ekar'nple- 'may be ja conventional one-shotr'n'ultivibr'ator, inwhich'- theY widthv`of the individual pulses' is `converted tov auniform selected value for subsequent utilization as will be `explainedhereinafter.- 4

Signals from receiving elements B and C are processed' in' a mannersimilar to the signal from receiving element Ar The signal fromreceiving element B is amplified in amplifier 15, converted to pulses inpulse generator 16, and widened-in pulse Widener 17 to fthe same widthasV the output' gpulses from pulsev generator 7. Likewise the sig-V nalfronrreceiving element C is ampliiied in amp-liner 25, converted to apulse train in pulse generator 26, land widened to the selected valueinpulse Widener 27. Control 250 which may'for' example vary the gridcircuit time constant, allows variation"-` inthe width of the outputpulses from pulse wideners 75, I7, and 27, for reasons Which'will appearhereinafter.

TheT outputs of-,p'ulse wideners 7,- 17, and 27, areYV fed tovganged'variable delay devices 8,- 81,- and 82, respec` Ytors-maybtefused, a'prefer'red form of variable'delay device-for'accomplishing -this purpose is a cathode ray tube typeof signalstorage-and play-back device, wherein signals tobe` delayed are recordedon theface of a cathode ray oscilloscope by a'irioving electron beam,`and played back-from the face of the oscilloscope by another'movingVelectron bearri tracesA fthe path`of the recording beam at? a, timelater than-the recording beam by an amount equal to the desired delay.Devices of this type are well known to the prior art, one such devicebeing fully illustrated and its mode of operation fully disclosed in thepatent to Riesz and Wertz 2,245,364. Because of the full disclosure ofvall details of such a signal delay device in that patent, only 'asimplified disclosure of the essential elements of such a delay devicewill be given in the present application.

Referring to Figure 2, a device of the type shown in signal delayrequired by the present invention, is shown at 40, and includes twocathode ray tubes 41 and 42 disposed in face to face relationship andseparated by a dielectric plate 42A. Cathode ray tube 41 constitutes asignal recording device and cathode ray tube 42 constitutes a signalplayback device. Tube 41 includes cathode 43, electron beam intensitycontrol grid 45, vertical deection plates 47 and 48, and horizontaldeflection plates 49 and 50. Vertical deflection plate 47 of cathode raytube 41 is connected to a sine Wave source designated as sweeposcillator 53. Horizontal deflection plate 49 is also connected througha conventional 90 phase shifter 44, to oscillator 53. This provides acircular sweep of the electron beam of tube 41 at the frequency of thesine wave output of oscillator 53. The frequency of'oscillator 53 issignificant, and will be explained more fully hereinafter. As indicatedin Figure 2 by the lead from oscillator 53 to theother delay devices, itis desirable to either synchronize the sweep oscillators of the threedelay devices 8, 81, and 82 or to use a common sweep oscillator for thethree delay devices to insure equal sweep frequencies for each.

Input signals to be delayed, such as for example the signal pulses frompulse Widener 7, are applied to the intensity control grid 45 of therecording tube 41. Such signals arerecorded on the face of the tube 41along the circular path described by the electron beam. Since therotating beam successively erases preceding signals as it records freshsignals, the maximum length of signal time which can be recorded on theface of tube 41 is equal to the time required for one revolution of theelectron beam,'which is equal to the period of one cycle of the outputof oscillator 53. Cathode ray tube 42 is provided with cathode 131,vertical deflection plates 132 and 133, horizontal deflection plates 134and 135, and electron collector anode 136. The vertical and horizontaldeflection plates of tube 42 are also connected in quadrature phaserelationship by means of 90 phase shifter 137, and supplied with thesine wave output of oscillator 53 through fixed phase shifter 61 andvariable phase shifter 62.

The electron beam of cathode ray tube 42 is therefore made to rotate ina circular path coincident with the path of the electron beam of tube41. However, this rotating playback beam of tube 42 is delayed relativeto the recording electron beam of tube 41 by the amount of phase shiftimposed by phase shifter 61 and 62. When the delayed beam of tube 42scans a signal recorded by tube 41, an output signal isl produced bysecondary emission to collector anode 136 of tube 42.

`Phase shifter element 61 is preferably of such value as to provide afixed phase shift of the sine wave output ofphase scan oscillator 53.Phase shifter 62 may be of any conventional type capable of providing asmooth continuous phase shift from zero to approximately 180, variablein aliner fashion. The exemplary phase shifter shown in Figure 2 forthis purpose is a conventional goniometer type of phase shifter,consisting of two fixed coils 141 and 142 oriented in quadrature, andone movable coil 143 mounted for rotation through the fields of thefixed coils. In such a goniometer type of phase shifter the input signalis connected across the fixed coils, and the rotating coil is'mechanically rotated, as by shaft 83, within the field ofthe fixedcoils, to provide an output signal from the rotating coil whose phase isdelayed smoothly relative to the phase of the input signal by an YPatent 2,245,364, suitable for accomplishing the variable 4 amount whichvaries linearly in proportion of the degree of rotation of the fixedcoil.

Returning to Figure l, for each delay device there is a mechanical driveshaft equivalent to the shaft 83 shown' in Figure 2 for driving therotating coil 143 of phase shifter 62. These mechanical drive shafts todelay devices 8, 81 and 82, are represented by broken lines 160, 161Hand162. Drive shaft 160 is connected to driving motor 68 through rack andpinion 65, scotch yoke 66, and eccentric64. Similarly, drive shafts .161and 162 are separately connected to motor 68 through similar racks andpinions 164, 165, scotch yokes 166, 167, and eccentrics 168, 169,respectively. `Eccentrics 64, 168 and 169 are spaced 120; forA reasonswhich will appear hereinafter.

By-analogy to the mannerinwhich the playback beam of tube 42 is delayedbehind the record beam of tube 41 in accordance with the angularposition of phase shifter rotor'143 and sh'aft I83, it will be apparentthat the amounts by which the respective signals from pulse wideners 7,17, and 27 are delayed vary in accordance with the langular positions ofrespective shafts 160, 161 and In order to recover selectively onlythose signals Whose direction of arrival at the three receiving elementscoincides with the selected reception bearing, it is necessary toeliminate all signals which do not emerge simultaneou-sly from the threevariable delay devices 8, 81 and 82. This elimination of extraneoussignals is accomplished in a coincidence gate 110, to which the outputsof delay devices 8, 81 and 82 are connected.

Reference is now made to Figure 3 wherein a preferred form ofcoincidence gate is shown schematically. Coincidence-gate -110 is of thesignal amplitude selective type. It includes two pairs of triodes 111,113, and 115, 119, each .pair having their cathodes tied together andplates tied together. The output of delay device 8 is connected to grid116 of triode 111, the output of delay device 81 is connected to grid117 of triode 113, the output of delay device 82 is connected to grid113 of v triode 119. The output of each delay device is arranged torepresent signals as positive pulses. The output from the parallelplates of triodes 111 and 113 is applied to the negatively biased grid114Y of tube 115 through a phase inverting transformer 112. The outputfrom the parallel plates of triodes 115 and 119 is applied through asecondphase inverting transformerl to the negatively biased grid ofanother triode 120.

In operation, the positive signals on grids 116 and 117 are combined andapplied through transformer 112 as positive pulses to grid 114 of -tube115. Only when said signals are overlapping do they reach grid 114 withsufficient amplitude to overcome its fixed negative bias. Similarly,signals reaching the plate of tube 11-5 combine with signals from delaydevice 82 and are applied as positive pulses to the grid of tube 120.Again only when these signals overlap do they overcome the fixednegative bias on tube `120. Thus the output tube of coincidence circuit110 is restricted to signals coinciding in time at the outputs of eachof the delay devices 8, 81, and 82. Or in other words, since the onlysignals passed by coincidence gate circuit 110 are those which arrive atgrids 116, 117 and 118 simultaneously, an output signal from gate 110indicates the arrival of signals at elements A, B and C so spaced intime as to be brought into coincidence by delay devices 8, 81 and 82,and hence having a direction of arrival corresponding to theinstantaneous selected reception bearing. It will be apparentthatthe'precision with which pulses from the outputs of delay devices 8,-81 and 82 must be related in time, in order to provide simultaneoussignals at the grids 116, 117 and 118 of coincident gate circuit 110, isdependent upon the width of these pulses. Very wide output pulses fromdelay devices 8, 81 and 82 need only be approximately coincident inorder to overlap sufficiently to produce an output pulse from gate 1 10,whereas .narrower pulses from delay devices'8, 81 Aand 82 must bemoreexactly related in time, or they will not overlap, jand 'will notproduce'any output pulse from gate 110. Thus if the output pulses frompulse wideners 7, 17 and `27 are suiiciently wide, those pulsesgenerated from signals received from a direction slightly diierent thanthe selected reception bearing which arrive at variable delay devices 8,81 and 82 with a timerelationship slightly different thanthatpassoci'ated with Vthe selectedreception bearing, will passthroghgate 110. l'

For this reason it maybe seen that the control 25,0, which varies thewidth of the output pulses from pulse4 wideners 7, 17 and 27,effectively/'varies the width of the directional zone about the selectedreception bearing from which 'signals received `can still produce outputpulses from gate 1710.

An explanation of the quantitative values of time by whichsignalsreceived by the three respectivev receiving elements-should bedelayed, as a function of the direction of signal arrival" or receptionbearing selected, will now be given. Figure 4 is a graph of the amountsof time by whichsignals from'icach of the three receiving elements mustbe delayed, plottedagainst the particular direction from vwhich lit isdesiredV to receive signals selectively, assuming the sides oftheequilateral triangle formed by the three receiving elements to beV of:such a length that the signal would require 100 microseconds to travel`this distance. As will be apparent from the: graph, signalsreceived'from a bearing of0.",` i.e., signals traveling in the directionfrom element A to 0, reach element A 57.8 microseconds before arrival at0.

A signal received from abearing of 90 arrives simultaneously at A and 0,and-when the selected receptionY bearing is 180, i.e., the directionfrom 0`to` A, signal arrival at element A `lags arrival at lby 57.8microseconds; Signal arrival at element B likewise varies from 57.8microseconds before arrival at. 0 when the bearing is 120, to 57.8,afterarrival at 0 when the bearing. isV

300. Arrivalat C precedes' arrival at 0 by 57.8 microseconds for bearing240 and lags arrival at 0 bythe same amount for bearing 60. Thus theamount ofV delay required toV compensate `for these differences inarrival times Varies,I through 360 of azimuth, from +57.8 microsecondsto -57.8 microseconds; a total of 1.15.6 microseconds.` Since thesignals cannot-,be delayed by a negative amount, the Variable delaydevices 8, 81 and 82 are arranged todelay their respective signalsthrough a range of from 0 tor 115.6 microseconds.

The goniometer phase Shifters' associatedwith Variable delay devices 8,81` and 82,y such as phase shifter 62 of Figure 2, are therefore sodesigned, in relation to the output. frequency of their associatedoscillators,y such as oscillator 53, that their maximum Vphase shiftequals a time delay of 115.6 microseconds. If phase shifter 62, forexample, provides phase shifts of from 0 to 180, then the frequency ofoscillator 53 should be selected so that the period of one-half cycleis.. 115.6 microseconds. This would require an output frequency of Thetime between arrival` of. a signal at any of the receiving elements A,B, or C,.and arrival at 0, variesv and 82' mustfal'so var ysinusoidally. For this reasonV scotch yokes 66, 1'66 and 167i areemployed to convert' the constant velocityV rotation ofthe'shaft' 'ofmotor 68j which are 120 to sinusoidally varyingangular displacement ofshafts 160, 1 61, and 162.` Y .l

As is also apparent from Figure 4, the amount of delay to be imposedupon receivedsig'nals reaches a maximum or minimum for the threeelements at respective bearings apart. iThis requires 1120" phaseseparation of the displacement-,of `shafts 160, 161 and 162, which isprovided by the arrangement of eccentrics 64, 168 and 169 in 120 spacedrelation. e

Thus, in operation, rotation'of the shaft of motor 68 varies the delayimposed by phase Shifters -8, 81 and 82, in a siusoidal manner, and in120 phase relation with each other. This varies through k360 of azimuththe selected receptionbearingfrom which direction signals arriving Vatelements A, B, and C are properly delayed to emerge simultaneouslyl fromthe outputs of variable delay devices 8,' 81 and 82.

The pulses which are united Vin coincidence gate 110 have the frequencyof the pulses originally produced by pulse generators 6, 16 and 26,whichV as explained heretofore is theV same asthe frequency-of the wavesignal intercepted by yreceiving eIementsA, B, and C.

To make the receiving system thusY far described frequency selective, apulse periodicity selective circuit r150 may be provided.V This circuit,asshown in Figure l, is fed by the output pulses from coincidence gateafter theyhave been shaped and invertedv by amplifier 149, and serves todiscriminate against all pulses in they output of gate 110 which do notyhave a periodicity corresponding to a. desired Vreceived signal.frequency. A

v The periodicity selective circuit. is shown, in greater detail inFigure 5. `Successive pulses from the output ofv coincidence gate 11'0are shaped and. inverted by amplifier 149 and simultaneously yfed 4to,grid of twintriode 201, grid 211 of another twiny triode 208 andv arefed to grid 203 of triode 201 through a variable delay line 202. Theplates and cathodes of twin. triodes 201and- 208 are tied together.Delay line 202 serves to establish the pulse spacing necessaryftoprovide simultaneous arrival of pulses at grids 200 and 203, which ofcourse produces a larger output pulse inthe plate circuitV 204 of thetwin triode than results from ai pulse at only one grid.

Output pulses from the plate circuit of twin triode 201 are connectedthrough another variable delay line 206, ganged with delay line 202, toalways present equal delay, to grid' 207 of another-twin triode 208.Pulses from the plate' circuit of tube 201` are. applied through` aphase inverting transformer 204 sincethey are. desired inVA positivepolarity at grid 207. Grid207 is so biased by battery 209 that only thelargerampli'tude pulses produced by simultaneous; pulses at the grids200 and 203 of twin triode 201 can cause conduction in the. right halfof tube 208. As stated above, the other grid 211 of `twin triode 208 isconnected directly byV conductor 212 to the` pulses from coincidencegate 110. Output pulses from plate circuit 214 of twin triode 208 arefed through a phase inverting transformer 214, to the grid 216 of anamplifier tube 215. The grid 216 of amplifier 215 is negatively biasedto pass only the larger amplitude pulses produced in plate circuit oftube 208 bythe simultaneous arrival of pulses at grids 211 and 207.

Thus a pulse appears at the output of' amplifier 215 only when therearrives at thev input' of the periodicity selector circuit 150 the thirdofthree` pulses spacedin accordance with the delay imposed by delaylines 202 and 206. Arrival of a fourth and iifth pulse, properly spaced,at the input of circuit 150 produces inturnA a` second and third outputpulse from amplifier 215.v But any break in. the trainv of properlyspaced pulses from gate 110 stops the output of pulses from amplifier21SV until three morerproperly spacedV pulses are supplied to circuit150. Y

Thus periodicity'selector circuit 150 operates to reject alll pulseswhich do not liaveltheperiodicity determined.

by delay lines202'and 206, and which do not arrive in trains of at leastthree. Of course additional twin triode stages identical to the two hereshown may be employed, which would increase the number of input pulsesin a trainnecessary to initiate an output from amplifier 215. Variationof the size of delay lines 202 and 206 varies the periodicity ofacceptable pulses from coincident gate 10, and thus eifectively tunesthe frequency of response of the receiving system. It will be understoodother delay devices, such as delay multivibrators, may be substitutedfor delay lines 202 and 206.

Referring again to Figure l, from the output of pulse periodicityselector 150, pulses are fed to any suitable received signal indicatingmeans 220. To correlate azimuth information with signal reception, theshaft of motor 68 is also coupled to indicator 220 to introduceinformation of the selected bearing and rate of sweep. Although manyindicating devices may be made suitable, a preferable arrangement is tointensity modulate a cathode ray tube with the selected signal pulsesand sweep said cathode ray tube with a circular sweep rotatingsimultaneously with motor 68. 4

For specific signal searching problems such as sector scanning, it maybe desirable to stop, reverse, or control the speed of scanning. Forthis purpose a motor speed and direction control means 22]; isincorporated with motor 68.

It will be understood that the principles of this bearing sensing systemare equally adaptable to selecting the bearing of signals reflected fromintentionally illuminated objects. g

Although certain specific embodiments of this invention have been hereindisclosed and described it is to be` understoodthat they are merelyillustrative of this invention and modications may of course be madewithout departing from the spirit and scope of the invention as definedin the appended claims.

The invention `described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. A directional wave signal receiving system comprising threeequilateral triangularly disposed omnidirectional receiving elements,three respective delay means for delaying the signals received by eachof said receiving elements, control means for varying the delays of saidthree delay means in 120 phase relation for varying the timerelationship of signals received by said three elements in accordancewith a selected reception bearing to superimpose signals received bysaid three elements from said selected reception bearing, and means fordisplaying superimposed signals.

2. A wave signal receiving system having a selected directionalVreception zone rotating through 360 of azimuth comprising threeomnidirectional receiving elements disposed in equilateral triangularrelation; three respective delay means for delaying the signals receivedby each of said receiving elements, control means for varying the delaysof said three delay means at a sinusoidal rate and in 120 phaserelation, coincidence gate means for recovering simultaneous signals inthe outputs of said respective delay means, and means for displayingsignals recovered by said coincidence gate means.

3. In a wave signal receiving system for receiving signals from aselected direction, three omnidirectional receiving elements disposed inequilateral triangular relation, respective' pulse generator means fedby the output of said respective receiving elements for generating pulsetrains having -the same periodicity as'the received wave signals,respective delay means for varying the phase relation of said respectivepulse trains in accordance with the relationship of the times of arrivalat said receiving elements of a signal fromsaid selected direction,whereby pulses generated from signals received from said selecteddirection are superimposed, and means for indis eating said superimposedpulses.

4. A directional-wave signal receiving system having a variable selectedreception direction comprising three receiving elements disposed inequilateral triangular relation, whereby the relationship of the timesof arrival of a received signal at said three receiving elements denotesthe direction of arrival of said signal relative to the orientation ofsaid receiving elements, signal delaying means remote from saidreceiving elements for relatively delaying signals received by saidthree elements in accordance with the arrival time relationship denotingsaid selected direction, whereby signals arriving yat said receivingelements from said selected direction are superimposed, means forcommunicating signals received -by said three receiving elements to saidsignal delaying means, and means for indicating superimposed signals.'5. In a wave signal receiving system having three omnidirectionalreceiving elements disposed Vin equilat; eral triangular relation, meansfor recovering only signals received from a selected directioncomprising pulse generator means for deriving from a received wavesignal respective pulses having a time relation equal to the relation ofthe respective times of arrival of said received wave signal at saidthree receiving elements, means for delaying said respective pulses byrespective amounts of time differing as the times of arrival at saidreceiving elements of a signal from said selected direction, wherebypulses derived from a signal received from said selected direction arebrought into coincidence, and means for indicating coincident pulses.

6. A wave signal receiving system for receiving sig-v nals from aselected direction comprising three omnidirectional receiving elementsdisposed in equilateral triangular relation, signal delay means for eachreceiving element for delaying signals received by each receivingelement an amount equal to the time for signals from said selecteddirection to travel between the nearest receiving element to saiddirection and the respective re-` ceiving element of each delay means,means communieating signals received by each of said elements to saidrespective delay means, coincidence gate means for superimposingsimultaneous input signals, means for connecting delayed signals to saidcoincidence gate means,

and means for indicating superimposed signals.

7. A wave signal receiving and indicating system for receiving signalsfrom a selected direction comprising three omnidirectional receivingelements disposed in equilateral triangular relation, signal delay meansfor each receiving element for delaying signals received by eachreceiving element, means communicating signals received by each of saidreceiving elements to said respective delay means, coincidence gatemeans for superimposing simultaneous input signals, means for connectingdelayed signals to said coincidence gate means, control means forvarying the delays of said several delay means sinusoidally in phasedrelation from zero to a maximum amount proportional to the spacing ofsaid receiving elements, whereby said selected direction is variedthrough 360, periodicity selective means fed by the output of saidcoincidence gate means for rejecting all of said superimposed signalsexcept those having a selected periodicity, and means for indicatingoutput signals from said periodicity selective means.

8. In a wave signal receiving system for receiving signals from aselected direction, three omnidirectional receiving elements disposed inequilateral triangular relation, respective pulse generator means fed bythe output of said respective receiving elements for generating pulsetrains having the same periodicity as the received wave signals,respective delay means for varying the phase relation of said respectivepulse trains, control means for varying the delays of said respectivedelay means sinusoidally inv120 phase relation from zero tol 9 a maximumamount proportional to the spacing of said receiving elements,coincident gate means fed by said delayed pulse trains for producing anoutput signal responsive only to the simultaneous input of a pulse fromeach delayed train, and means for indicating said output signa s.

9. A wave signal receiving and indicating system for receiving signalsfrom a selected direction comprising three omnidirectional receivingelements disposed in equilateral triangular relation, signal delaylmeans for each receiving element for delaying signals received by saidreceiving element, means communicating signals received by each of saidreceiving elements to said respective delay means, coincidence gatemeans for superimposing si- Y multaneous input signals, meansfor-connecting delayed signals to said coincidence gate-means, controlmeans for varying the delays of said several delay means sinusoidally in120 phased relation from zero to a maximum amount proportional to thespacing of said receiving elements, whereby said selected directionV isvaried through 360, and means for indicating signals superimposed bysaid coincidence gate means.

10. A directional Wave signal receiving system comprising threeomnidirectional signal receiving elements disposed in equilateraltriangular spaced relationship, signal delay means for each of saidreceiving elements, communication link means for conveying the signalsint, gtereepted by said respectivereceiving elements to said respectivedelay means, coincidence gate means for'prol ducing an output signalresponsive only to ak plurality means, periodicity selector meansfforrejecting kall sigrespective delay means in a sinusoidal manner fromzero 10 to a maximum amount proportional to the spacing of saidreceiving elements, and means for operating said respective controlmeans in phased relationship to superimpose signals received by -saidreceiving elements from any one direction, whereby said one direction isvaried through 360 of azimuth. v

1l. In a wave signal receiving system having three omnidirectionalreceiving elements disposed in equilateral triangular relation, meansfor recovering only signals received from a selected directional zonecomprising pulse generator means for deriving from a received `wavesignal respective pulses having a time relation equal to the relation ofthe respective times of arrival of said 151 received wave signal at saidthree receiving elements,

means for delaying said respective generated pulses by respectiveamounts of time differing as the times of arrival at said receivingelements of a signal from the center bearing of said selecteddirectional zone, whereby delayed pulses derived from a signal receivedfrom said center bearing are brought into exact coincidence and thosefrom other directions within said selected zone are approximatelycoincident, coincidence gate means fed by said delayed pulses forgenerating an output pulse responsive to the coincidence of a portion ofsaid delayed pulses, means for varying the duration of said generatedpulses, whereby delayed pulses derived from signals received from saidselected directional zone coincide during a portion of ftheirduration,and meansvforindicating-saidY output pulses. 'Y

l References Cited in the le of this patent UNITED STATES PATENTS

